Changing default separator for flattening params don't work if dictionnary has depth >1

[Galileo-Galilei]

Description

Changing the default hooks.nodes.sep `separator in the mlflow.yml does only work when the flattened dictionnary has depth one.

Context

How has this bug affected you? What were you trying to accomplish?

I was trying to change the default separator when flattening dict parameters.

Steps to Reproduce

1. Create a kedro project
2. Create mlflow.yml with kedro mlflow init
3. Change the default config:

# conf/local/mlflow.yml

hooks:
  node:
    flatten_dict_params: True  # Changed, default is True
    recursive: True  
    sep: "_" # Changed, default is "."
    long_parameters_strategy: fail 

# conf/base/parameters.yml

nested_params:
  a: 1
  b: 
    b1: 1
    b2: 2

4. Use this parameter in a node
5. Launch kedro run

Actual Result vs expected

The following parameters are then logged in mlflow:
-nested_params_a = 1
-nested_params_b.b1 = 1 (expected result is nested_params_b_b1 = 1)
-nested_params_b.b2 = 2 (expected result is nested_params_b_b2 = 1)

Solution:

The faulty line is

kedro-mlflow/kedro_mlflow/framework/hooks/node_hook.py

Line 136 in b3c1e26

new_value = flatten_dict(value) if recursive else value

Because arguments are not passed to the recursive call to flatten_dict